Method of controlling pressure in a well

ABSTRACT

A well venting system for controlling the pressure in a tubular element comprising a tubular element having an inner and outer surface forming a wall; and venting means to provide fluid communication between the inside of the inner surface and the outside of the outer surface.

The present application claims the benefit of U.S. Patent Application No. 61/554,648, filed Nov. 2, 2011, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a system and method for controlling the pressure in a well, especially when the well is outside of normal operation, for example, during a blowout, or when regaining control of a blowout well by a cap and shutting in.

BACKGROUND

Drilling liners are tubulars used to extend casings with, among other purposes, the purpose of achieving an increase in the fracture gradient to allow an increase in mud weight to be used during the drilling of high pressure oil or gas wells. Sometimes thin wall tubular are used for drilling liners to permit a larger inside diameter and thus the use of a larger hole size during well construction. However the thin wall drilling liners have a lower collapse rating. Collapse loads during normal drilling operations are low and so the low collapse rating of the liner is not normally a problem. However when a well blows out the collapse load can be very high as a result of the low internal pressure due to the flowing produced fluid pressure and high pressure external to the liner as a result of thermal expansion of the fluid behind the tubular.

U.S. Pat. No. 6,457,528 describes a method for preventing critical annular pressure buildup in an offshore well using a burst disk assembly. The burst disk ruptures at a predetermined pressure to protect the thin walled tubular during production from a well. Once the burst disk ruptures, it is open and there is no way to close it.

SUMMARY OF THE INVENTION

The invention provides a well venting system for controlling the external to internal pressure differential also known as the collapse load of a tubular element comprising a tubular element having an inner and outer surface forming a wall; and venting means to provide a path for fluid communication between the outside of the outer surface and the inside of the inner surface when the collapse rating of the tubular is approached.

The invention also provides a method to re-establish internal well integrity or the internal to external pressure differential also known as burst load of the tubular element by closing the venting system thus preventing fluid communication from the inside of the inner surface to the outside of the outer surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a system for controlling the pressure in a well.

DETAILED DESCRIPTION

The invention provides a system and method for controlling the pressure in a tubular element, typically a casing or liner, to prevent it from collapsing during a blowout. If a blowout occurs in a well, then the collapse load increases greatly and can damage the liner as described below. This could result in the inability to control the flow of hydrocarbons through the well and subsequent release to the environment. This can also make it difficult or impossible to cap and shut-in a well.

The buildup of pressure during a blowout is similar to the problems of annular pressure buildup that are described in U.S. Pat. No. 6,457,528. During the drilling of hydrocarbon production wells, a drill is used to bore through subterranean formations. As the drill bores into the formation, a drilling fluid known as a “mud” is pumped into the borehole and circulated through the hole and back to the surface. The mud is used to help lubricate and cool the drill bit, to remove cuttings and to provide sufficient hydrostatic pressure to prevent a blowout. A blowout can occur when the pressure in the formation exceeds the hydrostatic pressure of the mud because higher pressure gas and oil overcome the hydrostatic pressure of the mud and flow upward, typically exiting the well.

Different mud weights are used at different depths because the pressure in the formation increases as you drill deeper. As heavier mud weights are used, these tend to penetrate the shallower portions of the subterranean formation, so casing strings, and sometimes liners, are run into the borehole to provide a boundary between the borehole and the formation. In addition, the casing string is typically cemented into place by placing cement between the walls of the borehole and the casing string. As the well is drilled, different casing strings are used as a barrier between the formation and the well. These regions at the intersection of different casing strings have a region of casing that is typically exposed directly to the formation. Annular pressure buildup typically occurs as the result of producing hydrocarbons from the well, which heats the mud or fluid contained in the annular region. If the pressure exceeds the collapse load of the casing string or liner then the well integrity may be compromised thus putting the well at risk of being breached. U.S. Pat. No. 6,457,528 teaches the use of rupture disks that protect the tubular element, but at the loss of containment. Once the tubular disk ruptures, it cannot be replaced.

During a blowout, it is critical to protect burst integrity of the tubular elements that keep the hydrocarbon in the well which preserves the ability to cap and shut in the well. The burst integrity of the tubular elements may be compromised if the collapse rating of the element is exceeded during the period of the unrestricted flow also known as a blowout prior to capping the well.

The invention will be further described in relation to FIG. 1. FIG. 1 depicts a well drilled into a formation 10 that contains oil and gas. After a section of the well is drilled, a casing 12 is put into place and cemented with cement 14. A liner 18 hangs from liner hanger 16 and extends downward into the well. A portion of the liner is cemented with cement 20. Venting means 22 is located on the wall of the liner 18 and provides the ability to allow fluid communication between the inside of the liner 30 to the annulus 32.

During a blowout, hydrocarbons flow up the well uncontrollably to the surface or mud line. The resulting increase in well temperature causes the mud behind the liner to expand. The mud expansion causes the annulus pressure to increase towards the collapse rating of the liner.

The venting means 22 is activated or opened to allow fluid communication between the inside of the liner 30 and the annulus 32, thus equalizing the pressure of the annulus with the pressure in the well and the collapse load is reduced. The venting means may comprise any suitable venting means known to one of ordinary skill in the art, for example, valves, closeable vents, and any opening that can be opened and closed.

To stop the blowout, the well must be first capped and shut-in so that control can be regained. When the well is shut-in, the pressure in the well increases and the venting means closes. The liner has a sufficient burst rating to withstand the hydrocarbon pressure in the well and flow is stopped.

This prevents the release of any hydrocarbon to the environment as all of the hydrocarbon is contained within the well or the reservoir. It is preferred for the venting means to be able to remain closed during normal well construction operations, open when collapse loads pressures are high and then close as needed so that the tubular element can withstand the burst load pressure, and the well can maintain integrity. 

What is claimed is:
 1. A well venting system for controlling the pressure in a tubular element comprising a tubular element having an inner and outer surface forming a wall; and venting means to provide fluid communication between the inside of the inner surface and the outside of the outer surface.
 2. The system of claim 1 wherein the tubular element is a drilling liner or casing located in a well.
 3. The system of claim 1 wherein the venting means may be closed to prevent fluid communication between the inside of the inner surface and the outside of the outer surface.
 4. The system of claim 1 wherein the venting means may be opened to allow fluid communication between the inside of the inner surface and the outside of the outer surface when the pressure differential across the tubular element wall approaches the collapse rating of the tubular element wall.
 5. A method of controlling the pressure in a tubular element comprising providing a tubular element having an inner and outer surface and venting means that can provide fluid communication from inside the inner surface to outside the outer surface; and activating the venting means to equalize the pressure inside the inner surface with the pressure outside the outer surface.
 6. The method of claim 5 wherein the tubular element is a drilling liner or casing located in a well.
 7. The method of claim 5 wherein the venting means is activated when the pressure differential between the outside of the outer surface and the inside of the inner surface approaches the collapse rating of the tubular element.
 8. The method of claim 5 wherein the venting means is closed when the pressure differential is at a safe pressure for the tubular element. 